Have you read this so you understand how the 'speed' property works? A Basic LocationSensor Speedometer
If not do so immediately and also read Programming Your App to Make Decisions (the section on making Complex Conditions and Programming Conditions within a Condition,
Once you do understand, make a decision on whether this is going to work or not.
Incidentally, To convert m/sec to mph, Multiply the rate of meters per second by 2.2369. Example: 30 meters per second times 2.2369 equals 67.107, so 30 meters per second equals 67.107 miles per hour. (10m/s + 22.4 mph)